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Visal Sok

Publications and source records attributed to Visal Sok.

17 recordsLinked to original sources

The GOGREEN Survey: AI Powered Deconvolution Lifts The Veil on Outside-in Environmental Quenching at z > 1

A powerful probe of the physical processes that quench star formation in dense environments is determining where within galaxies star formation is suppressed. At high redshift, the spatial resolution of multi-band imaging limits such measurements. We use deep-learning-based deconvolution to recover spatially resolved optical and near-infrared photometry for galaxies in nine GOGREEN clusters at 1<z<1.4, using customized models trained on HST and JWST imaging. Using resolved rest-frame UVJ colors, we classify galaxies by the star-forming states of their inner and outer regions into predominantly star-forming, predominantly quiescent, inside-quenched, or outside-quenched. We find that 24% of galaxies classified as quiescent from their integrated colors retain significant star formation. The predominantly quiescent fraction increases with stellar mass and is higher in clusters than in the field while the cluster quenched fraction excess is, when limiting to predominantly quenched galaxies, approximately 20%. Contrary to previous GOGREEN studies using integrated colors, we find this excess to be independent of stellar mass, demonstrating that partially quenched galaxies can bias measurements based on integrated colors. Among galaxies retaining significant star formation, outside-quenched galaxies are substantially more common than inside-quenched galaxies and have a fraction excess of (22.8+/-5.8)% in clusters relative to the field at low masses. This provides evidence that clusters preferentially suppress star formation in the outskirts of low-mass galaxies. Our results demonstrate the importance of spatially resolved classifications for interpreting environmental quenching at z~1 and the potential of deep-learning-based deconvolution to recover such information from large ground-based imaging datasets.

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A New Window on the H{\alpha} Luminosity Function and Star Formation Rate Density from 1.2 < z < 6.6 from JWST Medium-Band Photometry

We present the first self-consistent measurement of the H{\alpha} luminosity function over a wide redshift range, covering cosmic noon into the epoch of reionization. Our analysis utilizes a novel method based on James Webb Space Telescope (JWST) NIRCam medium-band imaging. We combine data from the CANUCS, JWST in Technicolor, and JUMPS surveys which offer deep, uniform imaging (29.5-30 AB, 3{\sigma}) with extensive NIRCam medium-band coverage, reaching up to 29 total filters (up to 20 JWST) when including ancillary Hubble Space Telescope (HST) ACS and WFC3/UVIS data. The superb spectral energy distribution (SED) sampling enables precise, reliable photometric redshift estimation (outlier fraction 1.7\%, {\sigma} N_MAD = 0.039 for this sample) as well as accurate continuum subtraction and line flux measurement verified by spectroscopic follow-up (no systematic offset, 0.23 dex scatter). We measure the H{\alpha} luminosity function (LF) from 1.25 < z < 6.6 by tracing the H{\alpha} emission line in 11 medium-band filters. The combination of depth, redshift coverage, and statistical power is unique, providing strong constraints on the shape of the LF over almost three orders of magnitude in luminosity. Our dense SED sampling enables us to reliably correct for dust attenuation and derive dust-corrected star formation rate functions as well as the evolution of the cosmic star formation rate density over the full redshift range. We recover the peak at z ~ 2 and a decrease toward z = 6, though with a higher normalization more in line with recent IR measurements than UV, though eclipsing both. This potential tension will be addressed in future work utilizing larger surveys with MIR coverage to better constrain the bright end of the luminosity function and the effects of dust.

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Constraints on the Gas Geometry Surrounding Little Red Dots through Narrow-Line Diagnostics

Little Red Dots (LRDs) are a recently identified population of high-redshift sources, with a common interpretation being accreting black holes embedded within a spherical, optically thick gas envelope. Within this framework, some models propose that the continuum arises from the dense-gas envelope, where hard ionizing radiation from the central engine is reprocessed into a stellar-like photosphere with an effective temperature of $\sim$5000 K. This implies that both the UV continuum and narrow-line emission are then powered by the host galaxy rather than an exposed central engine. To test whether this is consistent with the observed narrow-line ratios, we analyze multiple line diagnostics for a sample of $\sim$20 LRDs with high signal-to-noise NIRSpec grating spectra. We find that at least 40\% of the LRDs have line ratios pointing toward high ionization parameter and electron temperature, with a further 15\% also falling in the AGN regime for the O\textsc{i}/H$\alpha$ diagnostic, indicative of harder ionizing radiation. These line ratios are incompatible with stellar photoionization from a star-forming host alone. This suggests lower density channels within the gas envelope through which high energy photons can escape and excite the surrounding narrow-line emitting gas. At the same time, most LRDs lack strong high-ionization line emission, with He\,\textsc{ii}/H$\beta$ $\lesssim0.1$, consistent with an ionizing spectrum softer than that of a standard AGN. Together, these results disfavour a uniform gas envelope with a covering fraction of unity, and instead point to a more complex geometry that gives rise to anisotropic ionizing radiation.

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Resolved Ages and Stellar Metallicities in Progenitors of Milky Way Analogs: A Closer Look at their Star Formation Histories since $z=5$

We present the evolution of the resolved mass-weighted age, stellar metallicity, and sSFR of 872 Milky Way Analog (MWA) progenitors up to redshift $z=5$ from the Canadian Unbiased Cluster Survey (CANUCS). The metallicity and mass-weighted ages were obtained via spatially resolved SED-fitting with the non-parametric code Dense Basis. We split the sample into mergers versus non-mergers using the merger parameter from the Gini-$M_{20}$ plane obtained through Gini-$M_{20}$ analysis of the morphology of the stellar mass maps with Statmorph. Across our redshift range, non-mergers have negative or flat average age gradients from $-0.022$ to 0.005 dex/kpc, and positive or flat sSFR gradients from $-0.089$ to 0.092 dex/kpc, consistent with inside-out assembly. The average $\log(Z/\Zsun)$ gradients for non-mergers range from $-0.029$ to 0.044 dex/kpc, however, positive gradients only appear between $2 < z < 3$. At every redshift epoch, mergers typically have flatter age gradients, more negative sSFR gradients, and similar metallicity gradients compared to non-mergers. We divide the property maps of ongoing mergers into separate regions based on their component galaxies, and find little to no difference between the components' average ages or metallicities, but the less massive of the merging system is on average $0.1-0.4$ dex higher in sSFR. Our results point to major mergers contributing some momentary disruption to the general trend of inside-out mass assembly, but does not upend the overall picture of MWA disks growing inside-out over cosmic time.

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CANUCS/Technicolor Data Release 2: A Catalogue of Galaxy Structural Parameters in up to 29 HST+JWST bands and a Multi-Wavelength Exploration of the Galaxy Size-Mass Relation at $0.6 < z \leq 4$

We present James Webb Space Telescope (JWST) results of a morphological study of galaxies in the CAnadian NIRISS Unbiased Cluster (CANUCS) and Technicolor surveys, observed in 19 medium- and broadband NIRCam filters in five CANUCS NIRCam Flanking Fields with rest-frame wavelength coverage between $\sim 0.2 - 3.2\mu m$. Using GALFIT, we measure the morphological parameters of $\sim$ 4,100 star-forming galaxies at $0.6 < z \leq 4$ with stellar masses of $8.5 < \text{log}(M_*/M_\odot) \leq 11.5$. This enables us to concurrently examine how galaxy size varies as a function of stellar mass, redshift, and rest-frame wavelength to provide a novel parametrization of the galaxy size-wavelength relation. Additionally, we analyze the evolution of the galaxy size-mass relation in the rest-frame optical and NIR with the introduction of wavelength as a free parameter. We report a gradient in the slope of the size-mass relation with respect to rest-frame wavelength with a critical crossover mass at $\sim 10^{9.5} M_\odot$. We propose this characteristic mass as the stellar mass at which galaxies transition between diffuse and compact morphologies. We concurrently present the data release of morphological measurements of the five CANUCS-Technicolor NIRCam Flanking Fields in which we provide structural parameters for $\sim$ 41,000 galaxies in up to 29 JWST+HST filters.

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A Population of Red Galaxies with Very Strong Emission Lines at $z > 5$ Revealed by the NIRCam Medium Bands: ''Classic'' LRDs, Dusty Star-Forming Galaxies, and a Missing Population of LRDs

The NIRCam medium-bands have proven to be efficient at identifying Emission Line Galaxies (ELGs) with high equivalent width (EW) H$\alpha$ and [OIII]+H$\beta$ emission lines. In this paper we exploit this efficiency to identify a sample of ELGs at $4.9 \lesssim z \lesssim 8.9$ using medium-band imaging from the CANUCS, Technicolor, and JUMPS surveys. We find that the ELGs exhibit a strong correlation between continuum color and emission line strength, such that galaxies with bluer UV/optical continua have stronger H$\alpha$ and [OIII]+H$\beta$ emission lines. We identify 26 galaxies that are outliers from this relation, which we call the Red Emission line Galaxies (REGs), because of their red continuum color and strong emission lines. We classify the REGs into three categories: 1) ''classic'' Little Red Dots (LRDs) selected with common literature criteria, 2) extended REGs, resolved in F444W and consistent with being Dusty Star Forming Galaxies (DSFGs), and 3) compact REGs, unresolved in F444W but not classified as LRDs. The compact REGs fail common LRD selections for several reasons, including faint continuua, contamination from emission lines (very strong [OIII]+H$\beta$), and UV/optical colors that are flatter than those of LRDs. We conclude that the compact REGs are likely LRDs that ''classic'' selection criteria miss, and are therefore missing from existing samples. Our results suggest that medium-band selection can provide more complete samples of these objects.

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Metal-Poor Gas Accretion Drives Giant Clump Formation at 0.6 < z < 2.6

The physical properties of kiloparsec-scale clumps in high-redshift star-forming galaxies (SFGs) contain crucial constraints on how they assemble. Building on recent work that indicates the presence of a metallicity offset in clumpy galaxies compared to nonclumpy SFGs, we analyze the chemical abundance in a large sample of ${\sim}300$ SFGs between $0.6 0$. We do not find a significant mass difference between these two clump populations. Finally, we compute the merger statistic using the Gini-M20 morphological parameters and find that the majority of clumpy galaxies are not classified as mergers based on their stellar mass maps. The results suggest that the clumpy nature of cosmic noon galaxies is linked to metal-poor gas accretion events that trigger star formation and dilute metallicities.

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The Stellar Mass and Age Distributions of Star-Forming Clumps at $0.5 < z < 5$ in JWST CANUCS: Implications for Clump Formation and Destruction

We investigate the resolved properties of star-forming clumps and their host galaxies at $0.5<z<5$ in the JWST CANUCS fields. We find that the fraction of clumpy galaxies peaks near $z\sim2$ for galaxies with masses of $\log(M_{g,*}/M_\odot)\geq10$, while galaxies with masses of $8.5 \leq \log(M_{g,*}/M_\odot) < 10$ show lower clumpy fractions with little redshift evolution. We identify and measure individual clump masses, finding that the aggregated clump stellar mass function (cSMF) follows a power-law slope of $\alpha = -2$ across all redshift bins, broadly consistent with \textit{in-situ} clump formation. However, when split by galaxy masses, the cSMF is found to be flatter ($\alpha\sim-1.6$) for massive galaxies and steeper ($\alpha\sim-2.3$) for lower mass galaxies, with little redshift evolution in both cases. We explore how different formation mechanisms and disruptive processes affect the shape of the clump mass function. In particular, we find that the cSMF slope is flatter with increasing gas fractions in younger clump populations ($<300$ Myr old), suggesting that higher gas availability leads to more massive clumps forming at the time of formation. Alternatively, many high-redshift galaxies in the sample have disturbed morphologies and simulations show that clumps of \textit{ex-situ} origins can flatten the cSMF slope. We also investigate the evolution of clump populations, where we find the cSMF slope become flatter as clumps evolve and age. We interpret this as an indication of the long-term survivability of massive clumps, with feedback mechanisms preferentially disrupting low-mass clumps. Overall, the galaxy-mass dependent cSMF and age distribution point to a complex history for clumps, involving different and competing mechanisms for their formation and destruction.

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Metal-Poor Star-Forming Clumps in Cosmic Noon Galaxies: Evidence for Gas Inflow and Chemical Dilution Using JWST NIRISS

The formation and evolution of galaxies are intricately linked to the baryon cycle, which fuels star formation while shaping chemical abundances within galaxies. Investigating the relationship between star formation and metallicity for large samples of galaxies requires expensive IFU surveys or sophisticated tools to analyze grism data. Here we analyze JWST NIRISS slitless grism data using Sleuth, a tool that forward models and infers spatially resolved physical properties from grism data, including observations from JWST NIRISS/NIRCam and future grism data like that from the Roman Space Telescope. Sleuth enables extraction of high-quality emission line maps from slitless spectra, overcoming contamination and spatially varying stellar populations, which previously limited such studies. Utilizing Sleuth with data from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), we investigated the relationship between metallicity and star formation in the star-forming clumps of galaxies at 0.6 < z < 1.35. We analyzed a sample of 20 galaxies, extracted high-quality emission line maps with Sleuth, and analyzed, in detail, the spatially resolved properties of star-forming clumps. Using $H\alpha$, [SII], and [SIII] emission line maps, we examined the spatially resolved metallicities, ionization, and star formation rates of our sample. Our findings reveal that these star-forming clumps show lower metallicities ($\sim$ 0.1 dex) than their surrounding galactic environments, indicating a metallicity dilution of 20 $\%$ within the clumps' gas. Our analysis indicates that these clumps exhibit intensified star formation and reduced metallicity, likely due to the inflow of metal-poor gas. These clumps illustrate the dynamic relationship between star formation and chemical enrichment within galaxies.

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MINERVA: A NIRCam Medium Band and MIRI Imaging Survey to Unlock the Hidden Gems of the Distant Universe

We present an overview of the MINERVA survey, a 259.8 hour (prime) and 127 hour (parallel) Cycle 4 treasury program on the James Webb Space Telescope (JWST). MINERVA is obtaining 8 filter NIRCam medium band imaging (F140M, F162M, F182M, F210M, F250M, F300M, F360M, F460M) and 2 filter MIRI imaging (F1280W, F1500W) in four of the five CANDELS Extragalactic fields: UDS, COSMOS, AEGIS and GOODS-N. These fields were previously observed in Cycle 1 with 7 - 9 NIRCam filters by the PRIMER, CEERS and JADES programs. MINERVA reaches a 5$\sigma$ depth of 28.1 mag in F300M and covers $\sim$ 542 arcmin$^2$, increasing the area of existing JWST medium-band coverage in at least 8 bands by $\sim$ 7$\times$. The MIRI imaging reaches a 5$\sigma$ depth of 23.9 mag in F1280W and covers $\sim$ 275 arcmin$^2$ in at least 2 MIRI filters. When combined with existing imaging, these data will provide a photometric catalog with 20-26 JWST filters (depending on field) and 26-35 filters total, including HST. This paper presents a detailed breakdown of the filter coverage, exposure times, and field layout relative to previous observations, as well as an overview of the primary science goals of the project. These include uncovering the physics of enigmatic sources hiding in current broadband catalogs, improving systematics on stellar mass functions and number densities by factors of $\gtrsim$ 3, and resolved mapping of stellar mass and star formation at 1 $< z <$ 6. When complete, MINERVA will become an integral part of the treasury deep field imaging datasets, significantly improving population studies with well-understood completeness, robust photometric redshifts, stellar masses, and sizes, and facilitating spectroscopic follow up for decades to come.

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CANUCS/Technicolor Data Release 1: Imaging, Photometry, Slit Spectroscopy, and Stellar Population Parameters

We present the first data release of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), a JWST Cycle 1 GTO program targeting 5 lensing clusters and flanking fields in parallel (Abell 370, MACS0416, MACS0417, MACS1149, MACS1423; survey area \tilda100 arcmin$^{2}$), with NIRCam imaging, NIRISS slitless spectroscopy, and NIRSpec prism multi-object spectroscopy. Fields centered on cluster cores include imaging in 8 bands from 0.9-4.4$\mu$m, alongside continuous NIRISS coverage from 1.15-2$\mu$m, while the NIRCam flanking fields provide 5 wide and 9 medium band filters for exceptional spectral sampling, all to \tilda29 mag$_{AB}$. We also present JWST in Technicolor, a Cycle 2 follow-up GO program targeting 3 CANUCS clusters (Abell 370, MACS0416, MACS1149). The Technicolor program adds NIRISS slitless spectroscopy in F090W to the cluster fields while adding 8 wide, medium, and narrow band filters to the flanking fields. This provides NIRCam imaging in all wide and medium band filters over \tilda30 arcmin$^{2}$. This paper describes our data reduction and photometry methodology. We release NIRCam, NIRISS, and HST imaging, PSFs, PSF-matched imaging, photometric catalogs, and photometric and spectroscopic redshifts. We provide lens models and stellar population parameters in up to 19 filters for \tilda53,000 galaxies in the cluster fields, and \tilda44,000 galaxies in up to 29 filters in the flanking fields. We further present 733 NIRSpec spectra and redshift measurements up to $z=10.8$. Comparing against our photometric redshifts, we find catastrophic outlier rates of only 4-7\% and scatter of $\sigma_{\rm NMAD}$ of 0.01-0.03.

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JWST Reveals a Candidate Jellyfish Galaxy at z=1.156

We report the discovery of COSMOS2020-635829 as a candidate jellyfish galaxy undergoing ram pressure stripping in a (proto)cluster at $z > 1$. High-resolution imaging from the James Webb Space Telescope reveals a symmetric stellar disk coupled to a unilateral tail of star-forming knots to the south. Using Gemini GMOS IFU observations, we show that these extra-planar continuum sources are embedded within an ionized gas tail that is kinematically connected to the disk of COSMOS2020-635829. If confirmed, this represents the highest-redshift discovery of a ram pressure stripped ionized gas tail. The tail sources are characterized by extremely young stellar populations ($\lesssim 100\,\mathrm{Myr}$), have stellar masses of ${\sim}10^8\,\mathrm{M_\odot}$, and star formation rates of $0.1\text{--}1\,\mathrm{M_\odot\,yr^{-1}}$. This work shows that ram pressure stripping can potentially perturb group and cluster galaxies at $z > 1$ and may contribute to environmental quenching even near Cosmic Noon.

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Resolved mass assembly and star formation in Milky Way Progenitors since $z = 5$ from JWST/CANUCS: From clumps and mergers to well-ordered disks

We present a resolved study of 877 progenitors of Milky Way Analogs (MWAs) at $0.3<z<5$ selected with abundance matching in the ten fields of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). Utilizing 18-21 bands of deep NIRCam, NIRISS, and HST photometry, we create resolved stellar mass maps and star formation rate maps via spectral energy distribution fitting with Dense Basis. We examine their resolved stellar mass and specific star formation rate (sSFR) profiles as a function of galactocentric radius, and find clear evidence for inside-out mass assembly. The total $\mstar$ of the inner 2 kpc regions of the progenitors remain roughly constant ($10^{9.3-9.4}\msun$) at $2<z<5$, while the total $\mstar$ of the regions beyond 2 kpc increases by 0.8 dex, from $10^{7.5}\msun$ to $10^{8.3}\msun$. Additionally, the sSFR of the outer regions increase with decreasing redshift, until $z\sim 2$. The median S\'ersic index of the MWA progenitors stays nearly constant at $n \sim 1$ at $2<z<5$, while the half-mass radii of their stellar mass profiles double. We perform additional morphological measurements on the stellar mass maps via the Gini-M20 plane and asymmetry parameters. They show that the rate of double-peak mergers and disturbances to galaxy structure also increase with redshift, with $\sim50\%$ of galaxies at $4<z<5$ classified as disturbed, and $\sim20\%$ classified as ongoing mergers. Overall, the early evolution of MWAs is revealed as chaotic, with significant mergers and high SFRs. Mass growth is primarily inside-out and galaxies become more disk-like after $z=3$.

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An Indication of Gas Inflow in Clumpy Star-Forming Galaxies near $z\sim1$: Lower Gas-Phase Metallicities in Clumpy Galaxies Compared to Non-Clumpy Galaxies

Despite the ubiquity of clumpy star-forming galaxies at high-redshift, the origin of clumps are still largely unconstrained due to the limited observations that can validate the mechanisms for clump formation. We postulate that if clumps form due to the accretion of metal-poor gas that leads to violent disk instability, clumpy galaxies should have lower gas-phase metallicities compared to non-clumpy galaxies. In this work, we obtain the near-infrared spectrum for 42 clumpy and non-clumpy star-forming galaxies of similar masses, SFRs, and colors at $z\approx0.7$ using the Gemini Near-Infrared Spectrograph (GNIRS) and infer their gas-phase metallicity from the {\nii} and {\halpha} line ratio. We find that clumpy galaxies have lower metallicities compared to non-clumpy galaxies, with an offset in the weighted average metallicity of $0.07\pm0.02$ dex. We also find an offset of $0.06\pm0.02$ dex between clumpy and non-clumpy galaxies in a comparable sample of 23 star-forming galaxies at $z\approx1.5$ using existing data from the FMOS-COSMOS survey. Similarly, lower {\nii}/{\halpha} ratio are typically found in galaxies that have more of their $\mathrm{UV_{rest}}$ luminosity originating from clumps, suggesting that \enquote{clumpier} galaxies are more metal poor. We also derive the intrinsic velocity dispersion and line-of-sight rotational velocity for galaxies from the GNIRS sample. The majority of galaxies have $\sigma_0/v_c \approx 0.2$, with no significant difference between clumpy and non-clumpy galaxies. Our result indicates that clump formation may be related to the inflow of metal-poor gas; however, the process that forms them does not necessarily require significant, long-term kinematic instability in the disk.

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A Measurement of the Assembly of Milky Way Analogues at Redshifts $0.5 < z < 2$ with Resolved Stellar Mass and Star-Formation Rate Profiles

The resolved mass assembly of Milky-Way-mass galaxies has been previously studied in simulations, the local universe, and at higher redshifts using infrared (IR) light profiles. To better characterize the mass assembly of Milky Way Analogues (MWAs), as well as their changes in star-formation rate and color gradients, we construct resolved stellar mass and star-formation rate maps of MWA progenitors selected with abundance matching techniques up to z $\sim$ 2 using deep, multi-wavelength imaging data from the Hubble Frontier Fields. Our results using stellar mass profiles agree well with previous studies that utilize IR light profiles, showing that the inner 2 kpc of the galaxies and the regions beyond 2 kpc exhibit similar rates of stellar mass growth. This indicates the progenitors of MWAs from $z\sim 2$ to the present do not preferentially grow their bulges or their disks. The evolution of the star-formation rate (SFR) profiles indicate greater decrease in SFR density in the inner regions versus the outer regions. Sérsic parameters indicate modest growth in the central regions at lower redshifts, perhaps indicating slight bulge growth. However, the Sérsic index does not rise above $n \sim 2$ until $z < 0.5$, meaning these galaxies are still disk dominated systems. We find that the half-mass radii of the MWA progenitors increase between $1.5 < z < 2$, but remain constant at later epochs ($z < 1.5$). This implies mild bulge growth since $z\sim 2$ in MWA progenitors, in line with previous MWA mass assembly studies.

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Resolved Stellar Mass Maps of Galaxies in the Hubble Frontier Fields: Evidence for Mass Dependency in Environmental Quenching

One of the challenges in understanding the quenching processes for galaxies is connecting progenitor star-forming populations to their descendant quiescent populations over cosmic time. Here we attempt a novel approach to this challenge by assuming that the underlying stellar mass distribution of galaxies is not significantly altered during environmental quenching processes that solely affect the gas content of cluster galaxies, such as strangulation and ram-pressure stripping. Using the deep, high-resolution photometry of the Hubble Frontier Fields, we create resolved stellar mass maps for both cluster and field galaxies, from which we determine 2D Sérsic profiles, and obtain Sérsic indices and half-mass radii. We classify the quiescent cluster galaxies into disk-like and bulge-like populations based on their Sérsic indices, and find that bulge-like quiescent galaxies dominate the quiescent population at higher masses ($M_\star > 10^{9.5}M_\odot$), whereas disk-like quiescent galaxies dominate at lower masses ($10^{8.5}M_\odot< M_\star < 10^{9.5}M_\odot$). Using both the Sérsic indices and half-mass radii, we identify a population of quiescent galaxies in clusters that are "morphological analogues" of field star-forming galaxies. These analogues are interpreted to be star-forming galaxies that had been environmentally quenched. We use these morphological analogues to compute the environmental-quenching efficiency, and we find that the efficiency decreases with increasing stellar mass. This demonstrates that environmental quenching is more effective on less massive galaxies and that the effect of environment on quenching galaxies is not completely separable from the effect of mass on quenching galaxies.

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Finite Resolution Deconvolution of Multi-Wavelength Imaging of 20,000 Galaxies in the COSMOS Field: The Evolution of Clumpy Galaxies Over Cosmic Time

Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFG) at 0.5<z<2 to an angular resolution of 0.3", and study their clumpy fractions. A comparison between the deconvolved and HST images across four different filters shows good agreement and validates the deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolved surface brightness and stellar mass density maps for these galaxies. We find that the fraction of clumpy galaxies decreases with increasing stellar masses, and with increasing redshift: from ~30% at z ~ 0.7 to ~50% at z ~ 1.7. Using abundance matching, we also trace the progenitors for galaxies at z ~ 0.7 and measure the fractional mass contribution of clumps toward their total mass budget. Clumps are observed to have a higher fractional mass contribution toward galaxies at higher redshift: increasing from ~1% at z ~ 0.7 to ~5% at z ~ 1.7. Finally, the majority of clumpy SFGs have higher specific star formation rates (sSFR) compared to the average SFGs at fixed stellar mass. We discuss the implication of this result to in-situ clump formation due to disk instability.

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